The purpose of this study is to determine the maximum tolerated dose (MTD) of 5-FU in the presence of doses of BAU determined in a previous phase I trial of elevate plasma uridine concentrations 4-fold in sustainable manner over 48 hours. The MTD will be determined for previously treated and chemotherapy-naive patients. Pharmacokinetic studies of both drugs will be performed. This is a phase I study and measurable of evaluable disease will not be required for enrollment, but response and response duration data will be obtained if appropriate.